1. Field of the Invention
The invention relates to circuit arrangements of hybrid junction devices.
2. Description of the Prior Art
While there are many radio frequency systems that operate at a single frequency, most operate on a band of frequencies or even a number of bands. The value of a given component is thus often greatly increased when it can be used over an extended range of frequencies.
Off-on rf switching and phase-shifting devices show increasing frequency sensitivity particularly above 300 megahertz. H. Seidel in U.S. Pat. No. 3,559,108 discusses the problem to some extent. As described by Seidel, a four-port hybrid junction in which two ports are connected as input and output terminals and the remaining two ports are terminated with diode switches, is much less affected by phase discrepancies at the switched terminals. For his purposes, Seidel discloses operating the two switches in opposite conductivity for one condition and in equal conductivity for the other condition.
If the quadrature junction circuit of Seidel were to be used as a phase inverter, then the diodes would have to have symmetrical conductivity for both phases, opposite conductivity being an "open switch" condition. The term "phase inverter" as used herein is defined to mean a device which can selectably change the phase of its output signal between two phases 180.degree. apart and implies no specific relation to the phase of the input signal.
Presently available diodes exhibit a reactance change with change in conductivity. This reactance change shows up as frequency sensitivity in conventional diode-switched junctions introducing phase-shift error and reducing switching efficiency away from the design center frequency.
Even in selected diodes, turn-on and turn-off will vary from the optimum differently with frequency change. Thus, though a system can be corrected for any given frequency, wide band operation is difficult to achieve.